U.S. patent application number 13/057926 was filed with the patent office on 2011-08-04 for molded object, heating device and method for producing a molded object.
This patent application is currently assigned to EPCOS AG. Invention is credited to Jan Ihle, Werner Kahr, Bernhard Steinberger.
Application Number | 20110186711 13/057926 |
Document ID | / |
Family ID | 41059733 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110186711 |
Kind Code |
A1 |
Ihle; Jan ; et al. |
August 4, 2011 |
Molded Object, Heating Device and Method for Producing a Molded
Object
Abstract
A mold (30), which has a first region (10) comprising an
electroceramic material and a second region (20) comprising a
structural ceramic material, is provided. A heating device with
this mold is also specified. Furthermore, a method for producing a
mold is provided.
Inventors: |
Ihle; Jan; (Grambach,
AT) ; Kahr; Werner; (Deutschlandsberg, AT) ;
Steinberger; Bernhard; (Seiersberg, AT) |
Assignee: |
EPCOS AG
Munich
DE
|
Family ID: |
41059733 |
Appl. No.: |
13/057926 |
Filed: |
July 24, 2009 |
PCT Filed: |
July 24, 2009 |
PCT NO: |
PCT/EP2009/059578 |
371 Date: |
April 25, 2011 |
Current U.S.
Class: |
249/78 ;
264/616 |
Current CPC
Class: |
C04B 2237/348 20130101;
B28B 7/24 20130101; C04B 2237/343 20130101; C04B 2235/6567
20130101; C04B 2237/34 20130101; C04B 2235/656 20130101; F02M 53/06
20130101; H01C 7/025 20130101; C04B 2235/77 20130101; C04B
2235/3262 20130101; C04B 2237/32 20130101; C04B 35/4682 20130101;
C04B 37/001 20130101; C04B 2237/346 20130101 |
Class at
Publication: |
249/78 ;
264/616 |
International
Class: |
B28B 7/42 20060101
B28B007/42; C04B 35/64 20060101 C04B035/64; B28B 1/14 20060101
B28B001/14; B28B 1/24 20060101 B28B001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2008 |
DE |
10 2008 036 836.9 |
Claims
1. A mold, comprising a first region, which has an electroceramic
material with a positive temperature coefficient of the electrical
resistance, a second region, which has a structural ceramic
material, and between the first region and the second region, an
interfacial region, in which the electroceramic material and the
structural ceramic material are sintered to one another.
2. The mold as claimed in claim 1, wherein the electroceramic
material has a perovskite structure.
3. The mold as claimed in claim 1, wherein the electroceramic
material has the structure
Ba.sub.1-x-yM.sub.xD.sub.yTi.sub.1-a-bN.sub.aMn.sub.bO.sub.3, where
x=0 to 0.5, y=0 to 0.01, a=0 to 0.01, b=0 to 0.01, M comprises a
divalent cation, D comprises a trivalent or tetravalent donor and N
comprises a pentavalent or hexavalent cation.
4. The mold as claimed in claim 1, wherein the electroceramic
material has a Curie temperature, which comprises a range from
-30.degree. C. to 340.degree. C.
5. The mold as claimed in claim 1, wherein the electroceramic
material has a resistivity at 25.degree. C. which lies in a range
from 3 .OMEGA.cm to 100 000 .OMEGA.cm.
6. The mold as claimed in claim 1, wherein the structural ceramic
material comprises an oxide ceramic.
7. The mold as claimed in claim 1, wherein the oxide ceramic is
chosen from a group which comprises ZrO.sub.2, Al.sub.2O.sub.3 and
MgO.
8. The mold as claimed in claim 1, wherein the first region, the
second region and the interfacial region have coefficients of
thermal expansion that differ from one another by less than
2*10.sup.-6/K.
9. The mold as claimed in claim 1, wherein the interfacial region
inhibits the diffusion of constituents of the electroceramic
material and of the structural ceramic material.
10. A heating device comprising a mold, which comprises: a first
region, which has an electroceramic material with a positive
temperature coefficient of the electrical resistance, a second
region, which has a structural ceramic material, and between the
first region and the second region, an interfacial region, in which
the electroceramic material and the structural ceramic material are
sintered to one another.
11. The heating device as claimed in claim 10, wherein electrical
contacting areas for producing a current flow in the mold are
arranged on the mold.
12. The heating device as claimed in claim 11, wherein the first
region of the mold is provided with the electrical contacting
areas.
13. A method for producing a mold comprising A) providing an
electroceramic starting material, B) providing a structural ceramic
starting material, C) producing a green body, which comprises a
first region, comprising the electroceramic starting material, and
a second region, comprising the structural ceramic starting
material, and D) sintering the green body to produce the mold, the
electroceramic starting material being transformed into an
electroceramic material with a positive temperature coefficient of
the electrical resistance.
14. The method as claimed in claim 13, wherein, in steps A) and B),
an electroceramic starting material and a structural ceramic
starting material that have coefficients of expansion which differ
by less than 2*10.sup.-6/K are chosen.
15. The method as claimed in claim 13, wherein, in method step C),
a molding method chosen from injection molding, multilayer
extrusion and film casting is used.
Description
[0001] The invention relates to a mold, a heating device which
comprises the mold and a method for producing a mold.
[0002] Media, for example fluids, can be heated by means of thermal
contact with materials that have a positive temperature coefficient
of the electrical resistance (PTC materials). Such PTC materials
can so far be formed as sheets or rectangular elements that consist
of a PTC material.
[0003] A problem to be solved is that of providing a mold that has
a high mechanical strength and chemical stability and comprises a
material with PTC properties. This problem is solved by a mold
according to patent claim 1. Further embodiments of the mold, a
heating device comprising a mold and a method for producing a mold
are the subject of further patent claims.
[0004] According to one embodiment, a mold which comprises a first
region, a second region and an interfacial region between the first
region and the second region is provided. The first region has an
electroceramic material with a positive temperature coefficient of
the electrical resistance and the second region has a structural
ceramic material. In the interfacial region, the electroceramic
material and the structural ceramic material are sintered to one
another. This provides a one-piece mold in which there is a
composite of an electroceramic material and a structural ceramic
material. Consequently, purely shaping components or shaping and
functional components can be combined in one mold.
[0005] Furthermore, the electroceramic material of the first region
of the mold may have a perovskite structure. The electroceramic
material may have the structure
Ba.sub.1-x-yM.sub.xD.sub.yTi.sub.1-a-bN.sub.aMn.sub.bO.sub.3. In
this case, x is chosen from the range 0 to 0.5, y from the range 0
to 0.01, a from the range 0 to 0.01, and b from the range 0 to
0.01. M may comprise a divalent cation, D a trivalent or
tetravalent donor and N a pentavalent or hexavalent cation. M may
be, for example, calcium, strontium or lead, and D may be, for
example, yttrium or lanthanum. Examples of N are niobium or
antimony. The electroceramic material may comprise metallic
impurities that are present with a content of less than 10 ppm. The
content of metallic impurities is so small that the PTC properties
of the electroceramic material are not influenced.
[0006] The electroceramic material in the mold may also have a
Curie temperature, which comprises a range from -30.degree. C. to
340.degree. C. Furthermore, the electroceramic material may have a
resistivity at 25.degree. C. which lies in a range from 3 .OMEGA.cm
to 100 000 .OMEGA.cm.
[0007] As a result of the use of an electroceramic material with a
positive temperature coefficient of the electrical resistance, the
mold comprises the first region, which is heated by applying a
voltage and can give off this heat to the surroundings. In this
case, this region has a self-regulating behavior. If the
temperature in the first region reaches a critical value, the
resistance in this region also increases, so that less current
flows through the first region. This prevents further heating-up of
the first region, so that no additional electronic control of the
heating power output has to be provided.
[0008] The structural ceramic material of the second region of the
mold may comprise an oxide ceramic. The oxide ceramic may be chosen
from a group which comprises ZrO.sub.2, Al.sub.2O.sub.2 and MgO.
The use of further oxide ceramics is possible as well. These oxide
ceramics have high mechanical strength, for example with respect to
abrasion, and a high chemical resistance, for example with respect
to acids and bases. Furthermore, they are suitable for food contact
applications and can without any hesitation be brought into contact
with materials, for example media to be heated, that must not be
contaminated.
[0009] If the mold is used for example in a heating device, the
second region of the mold may be molded in such a way that it is
present at locations where it is in contact with the medium to be
heated and/or where a high degree of abrasion occurs.
[0010] This provides a mold in which there is a separation between
the electrical function in the first region and the mechanically
stable structural component in the second region.
[0011] Furthermore, the mold can be produced by means of injection
molding, and consequently can be molded in any geometric form that
is necessary for the respective structural surroundings. If the
mold is used in a heating device, the first region can consequently
be molded in such a way that it can be arranged in regions of the
structure that are difficult to access. In this way, for example, a
medium can be heated efficiently with very short heating-up times
and low heating power outputs.
[0012] Furthermore, the first region, the second region and the
interfacial region may have coefficients of thermal expansion that
differ from one another by less than 2*10.sup.-6/K. This in effect
chooses a material combination that has suitable phases in the
interfacial region between the first region and the second region.
"Phases" may comprise mixed crystals of the electroceramic and
structural ceramic materials. Such mixed crystals may be, for
example, barium-lead-zirconium titanates if zirconium oxide is
chosen as the structural ceramic material. In the case of
Al.sub.2O.sub.3 or MgO as the structural ceramic material, the
mixed crystals may correspondingly be barium-aluminum titanate or
barium-magnesium titanate. Depending on the distance from the first
region and the second region, the mixed crystals pass fluently into
the electroceramic material and the structural ceramic material.
"Suitable" means in this context that the interfacial region has
coefficients of expansion similar to the adjacent regions. The
coefficients of expansion of the materials used in the first
region, second region and the interfacial region may be adapted to
one another in such a way that no stress cracks form under
heating.
[0013] Furthermore, the interfacial region of the mold may inhibit
the diffusion of constituents of the electroceramic material and of
the structural ceramic material. Constituents may be, for example,
anions or cations that are present in the electroceramic material
or the structural ceramic material. This avoids mutual impairment
of the functional and/or structural properties of the first and
second regions.
[0014] Also provided is a heating device which comprises a mold
with the aforementioned properties. The heating device may comprise
the mold on which electrical contacting areas for producing a
current flow in the mold are arranged. In this case, the first
region of the mold may be provided with the electrical contacting
areas. This produces the current flow in the first region of the
mold.
[0015] With a heating device which comprises a first, functional
region and a second, structural region, the separation of medium to
be heated and the electroceramic material can be realized. This
allows the regions of the heating device that are subjected to
mechanical and/or abrasive loads to be isolated from the electrical
function. The use of the structural ceramic material in the second
region also allows media that must not be contaminated to be
heated. Dissolving of constituents of the first region by the
medium to be heated is also prevented, by the second region being
present between the first region and the medium to be heated.
[0016] Also provided is a method for producing a mold. The method
comprises the method steps of
A) providing an electroceramic starting material, B) providing a
structural ceramic starting material, C) producing a green body,
which comprises a first region, comprising the electroceramic
starting material, and a second region, comprising the structural
ceramic starting material, and D) sintering the green body to
produce the mold, the electroceramic starting material being
transformed into an electroceramic material with a positive
temperature coefficient of the electrical resistance.
[0017] With this method, a one-piece mold that has regions with
functional properties and with structural properties can be
provided in a molding process. The joint production of these
regions avoids having to produce a number of individual components
and fasten them to one another with form-fitting engagement. The
joint molding and joint debinding and sintering of the
electroceramic starting material and the structural ceramic
starting material have the effect that at least two regions that
have the desired electrical and mechanical properties are formed in
a mold, are arranged in form-fitting engagement and are sintered to
one another.
[0018] In method step A), an electroceramic starting material which
has a structure having the formula
Ba.sub.1-x-yM.sub.xD.sub.yTi.sub.1-a-bN.sub.aMn.sub.bO.sub.3 can be
provided. In this case, x comprises the range 0 to 0.5, y the range
0 to 0.01, a the range 0 to 0.01, b the range 0 to 0.01, M a
divalent cation, D a trivalent or tetravalent donor and N a
pentavalent or hexavalent cation. This starting material can be
transformed into an electroceramic material with a positive
temperature coefficient of the electrical resistance and has a
perovskite structure.
[0019] In order to produce the electroceramic starting material,
with less than 10 ppm of metallic impurities, it can be produced
with molds which have a hard coating in order to avoid abrasion. A
hard coating may, for example, consist of tungsten carbide. All the
surfaces of the molds that come into contact with the
electroceramic starting material may be coated with the hard
coating.
[0020] In this way, an electroceramic starting material that can be
transformed into an electroceramic PTC material by sintering can be
mixed with a matrix and processed to form granules. These granules
can be injection-molded for further processing.
[0021] The matrix in which the electroceramic starting material is
incorporated and which has a lower melting point than the
electroceramic starting material may in this case make up a
proportion of less than 20% by mass with respect to the
electroceramic starting material. The matrix may comprise a
material chosen from a group which comprises wax, resins,
thermoplastics and water-soluble polymers. Further additives, such
as antioxidants or plasticizers, may likewise be present.
[0022] Furthermore, in method step B), the structural ceramic
starting material can be mixed with a matrix and processed to form
granules which can be injection-molded for further processing.
[0023] The matrix in which the structural ceramic starting material
is incorporated and which has a lower melting point than the
structural ceramic starting material may in this case make up a
proportion of less than 20% by mass with respect to the structural
ceramic starting material. The matrix may comprise a material
chosen from a group which comprises wax, resins, thermoplastics and
water-soluble polymers. Further additives, such as antioxidants or
plasticizers, may likewise be present.
[0024] During the sintering in method step D), the electroceramic
starting material is transformed into the electroceramic material
of the mold that has a positive temperature coefficient of the
electrical resistance and the structural ceramic starting material
is transformed into the structural ceramic material of the mold and
the matrix is removed.
[0025] A material which can be transformed by sintering into an
oxide ceramic chosen from a group which comprises ZrO.sub.2,
Al.sub.2O.sub.3 and MgO may be chosen as the structural ceramic
starting material.
[0026] When choosing the electroceramic starting material and the
structural ceramic starting material, a suitable match should be
found between the molding properties and the sintering conditions.
For example, the materials should be sintered with similar maximum
temperatures, holding times and cooling gradients. In order to
realize joint sintering of the electroceramic starting material and
the structural ceramic starting material in the same process, the
sintering temperature can be increased in the case of the
electroceramic starting material and lowered in the case of the
structural ceramic starting material by suitable measures. Suitable
measures are, for example, adding oxides with calcium, strontium,
lead or zirconium to the electroceramic starting material or adding
oxides with elements from the group of alkalis, alkaline earths,
titanium oxide or silicon oxide, for example oxides with yttrium,
calcium or cerium, to the structural ceramic starting material.
This allows the physical parameters of the electroceramic starting
material and of the structural ceramic starting material to be
modified in such a way that a common process window can be achieved
for processing the two materials.
[0027] In method steps A) and B), for example, the electroceramic
starting material and the structural ceramic starting material can
be chosen such that they have coefficients of expansion which
differ by less than 2*10.sup.-6/K. In the joint sintering in method
step D), an interfacial region in which the electroceramic material
and the structural ceramic material are sintered with one another
is formed between the two materials. For this purpose, excessive
amounts of low-melting eutectics should not be formed in the
interfacial region during the sintering. In this way, suffient
stability of the form of the mold is ensured.
[0028] In method step C), a molding method chosen from injection
molding, multilayer extrusion and film casting may be used. By
means of injection molding, for example, it is possible to provide
molds in any desired forms, which can be adapted to the respective
conditions and structural surroundings.
[0029] The invention will be explained in still more detail on the
basis of the figures and exemplary embodiments.
[0030] FIG. 1 shows the schematic side view of an embodiment of a
heating device,
[0031] FIG. 2 shows the schematic, perspective view of a second
embodiment of a heating device.
[0032] FIG. 1 shows the schematic side view of a first embodiment
of a heating device. This comprises a first region 10 and a second
region 20, which together form the mold 30. Arranged on the first
region 10 are two electrical contacting areas 40 and 45, which can
be contacted by way of electrical terminals 15. The first region 10
and the second region 20 are sintered to one another, so that
additional fastening of the two regions to one another is not
necessary and the mold 30 is formed as one piece.
[0033] The region 10 comprises an electroceramic material of the
structure
Ba.sub.1-x-yM.sub.xD.sub.yTi.sub.1-a-bN.sub.aMn.sub.bO.sub.3, which
furthermore may be doped with a rare earth, such as for example
calcium, strontium, lead or zirconium. With this electroceramic
material, the first region has a positive temperature coefficient
of the electrical resistance.
[0034] The second region 20 may comprise a structural ceramic
material, for example an oxide ceramic, which likewise may be doped
with elements from the group of alkalis, alkaline earths, titanium
or silicon, for example yttrium, calcium or cerium.
[0035] In this way, the mechanical and chemical load-bearing
capabilities of the structural ceramic material are combined with
the electrical functionality of the electroceramic material in a
one-piece mold 30. In the production of the mold 30, a joint
joining process (CIM, Ceramic Injection Molding) is used to bond
together the electroceramic and structural ceramic materials that
have been made to match one another in their coefficients of
thermal expansion. The coefficients of thermal expansion must in
this case have differences less than 2*10.sup.-6/K, which can be
achieved by the appropriate dopings of the materials, over the
entire temperature range from 1260.degree. C., where there is a
mixture of solid BaTiO.sub.3 and liquid BaTiSiO.sub.5, to room
temperature, that is to say even below the liquid-phase sintering
temperature. According to the composition, liquid phases of the
electroceramic and structural ceramic materials may occur at
temperatures from 940.degree. C. to 1670.degree. C.
[0036] In the critical temperature range with great stresses, the
ceramic materials should be cooled slowly, for example by
0.2.degree. C. per minute. The critical temperature range may in
this case lie between room temperature and 1260.degree. C.
[0037] In order to achieve sintering capabilities up to densities
of 99% of the structural ceramic material, grain sizes of less than
1 .mu.m before the sintering process, or sintering aids, such as
for example SiO.sub.2, TiO.sub.2 or FeO, may be used. In this way,
sintering temperatures of less than 1400.degree. C. are possible
with sintering times of less than 120 minutes.
[0038] If the electroceramic materials comprise amounts of lead,
very low sintering temperatures below 1300.degree. C. can be used
to prevent enrichment of the lead in the structural ceramic
material.
[0039] Amounts of binder in the electroceramic and/or structural
ceramic material as well as pressing or joining forces are set to
similar shrinkage values during the debinding and sintering, which
leads to amounts of binder of over 1% by weight.
[0040] FIG. 2 shows the schematic perspective view of a further
embodiment of the heating device. Here, the first region 10 and the
second region 20, which together form the mold 30, are formed as a
pipe, the first region 10 surrounding the second region 20. On both
end faces of the first region 10 there are electrical contacting
areas 40 and 45. The electrical terminals 15, by way of which the
contacting areas 40 and 45 are contacted, are not shown here for
the sake of overall clarity. Through such a pipe there may be
passed, for example, a medium that is heated when a voltage is
applied through the first region, while the second region 20
provides the mechanical and chemical stability of the mold 30
during the flowing of the medium through the pipe. Contamination of
the medium to be heated or destruction of the first region by the
medium are inhibited, since the second region 20 is present between
the medium to be heated and the first region 10.
[0041] The embodiments shown in the figures and exemplary
embodiments can be varied as desired. It should also be taken into
consideration that the invention is not restricted to the examples
but allows further refinements that are not specified here.
LIST OF DESIGNATIONS
[0042] 10 first region [0043] 15 electrical terminal [0044] 20
second region [0045] 30 mold [0046] 40 electrical contacting area
[0047] 45 electrical contacting area
* * * * *